Co-sleeping has been a long-standing controversial topic among parenting communities. Most of the research that discourages co-sleeping are based on pediatric sleep models, which emphasize solitary sleep as the norm. This is also consistent with endorsement of avoiding bed-sharing by the American Academy of Pediatrics and the National Health Service in the UK to minimize the risk of Sudden Infant Death Syndrome (SIDS) and other sleep-related incidents [4].

However, research shows that co-sleeping is more common among infants in Asian countries, with a prevalence rate of 86.47% [5], compared to just 21.95% among infants living in Western countries. This is consistent with findings from our research team, which has consistently found higher rates of co-sleeping in South Korea. In a cross-sectional study comparing co-sleeping rates among children in the USA, Australia, and South Korea, the prevalence of co-sleeping was lowest in the USA at 13% when the infant was six months old, compared to 54% in Australian mothers and 77% in Korean mothers. The substantial differences in co-sleeping prevalence found in our study remained consistent with older children, with 77% of Korean mothers reporting co-sleeping, followed by 20% of Australian mothers and only 4.5% of U.S. mothers for children at 24 months [6]. In a separate longitudinal cohort study within South Korea, we followed children annually starting from 3 years of age for 5 years across 6 time points. At the beginning, co-sleeping rates (defined by sleeping with parents or siblings on the same bed surface at a minimum of 2 or more times per week) were 95%, and persisted throughout the study, with 71.3% reported continuing to co-sleep at 7–8 years of age. However, despite these differences, SIDS incidences between South Korea and other Western countries such as USA. and Australia do not differ. In fact, incidents of SIDS in South Korea are estimated to be 0.22–0.36 per 1000 infants for SIDS in 2020, which is lower compared to 0.31 for the USA. and 0.3 in Australia [7]. While these differences may be affected by differences in classification methods, autopsy practices, and reporting systems between countries, the statistics do not differ drastically.

These statistics highlight the need to re-evaluate the definition and understanding currently used in the literature of co-sleeping. First, many studies have dichotomized co-sleeping when investigating its effects on child sleep or developmental factors, but we need to question whether this conceptualization mirrors the real world. Many parents would agree that co-sleeping is hardly clear-cut. The decision to co-sleep may be based on several parental or child factors. For example, Owens and Mindell (2005) [8] differentiate between lifestyle co-sleeping and reactive co-sleeping. Lifestyle co-sleeping refers to when parents choose to share their bed with their child for emotional bonding or cultural issues. In contrast, reactive co-sleeping may be a parental reaction to a child waking up frequently during the night, and sleeping separately may require frequent parental interventions to the point where everyone may get better sleep by sleeping together, or a result of parental general anxiety associated with the child’s sleep. A child might start out in their own bed at the beginning of the night but end up in the parent’s bed at some point in the night because of an awakening, which may be incidental or habitual. Other children may go for long stretches of time sleeping independently, but circumstances (e.g., being sick, experiencing transitions which require emotional soothing) may lead to intermittent co-sleeping. Defining co-sleeping as a yes/no question is not sufficient in understanding the multidimensional nature of all cultural norms, caregiving practices, and individual and environmental factors that contribute to the decision of co-sleeping.

Second, most studies investigating the effects of co-sleeping studies have resulted in equivocal results, and have fueled controversy. The mixed literature is likely due to the lack of consensus on the definition of co-sleeping, using unvalidated tools and cross-sectional study designs. Longitudinal studies of co-sleeping will enable us to provide guidelines on developmental timing, pattern variability, or subgroup variabilities. In regards to developmental timing, sleep during childhood undergoes rapid changes across developmental stages, yet longitudinal studies on co-sleeping are lacking. Previous studies have not thoroughly explored whether co-sleeping might be beneficial at certain stages but potentially less optimal at others. For example, one finding from a longitudinal study of co-sleeping over five years by our research team found that children who had sleep anxiety between ages 4–6 were significantly associated with co-sleeping one year later, but between ages 5 to 8, co-sleeping was significantly associated with sleep anxiety at the subsequent time point, but the opposite relationship was not significant (Shin et al., unpublished data). In addition, most co-sleeping children do eventually end up sleeping independently during their lives. If so, at what age or developmental stage does co-sleeping transition from beneficial to potentially disadvantageous, particularly regarding its impact on developmental trajectories (e.g., autonomy, emotional regulation)? With regard to pattern variability, does intermittent co-sleeping carry different risks or benefits compared to continuous co-sleeping arrangements, and are there critical duration thresholds that influence outcomes? With regards to subgroup vulnerabilities, are certain children (e.g., those with neurodevelopmental differences, anxiety tendencies, or specific family dynamics) disproportionately affected by co-sleeping practices, or should guidelines prioritize universal recommendations?

Third, when co-sleeping presents in the context of a pediatric sleep problem, it may be important to further investigate the influence of parental factors. Research conducted by our team revealed a significant correlation between parents’ dysfunctional beliefs and attitudes about their own sleep and their misperceptions regarding their child’s sleep (r=0.35, p<0.01) [9]. This suggests that parents’ beliefs about their child’s sleep may, in part, be shaped by rigid or negative thought patterns stemming from their own sleep difficulties. Sleeping independently in children is closely linked to the acquisition of self-regulation skills. This process is not inherently innate but rather a developmental journey that unfolds during early childhood. It is fostered through parental interactions that provide appropriate challenges and opportunities for mastery, allowing children to cultivate self-regulatory abilities. Parents who hold negative views about sleep may be likely to choose co-sleeping to offer immediate comfort when a child is experiencing sleep-related anxiety, such as fear of the dark or difficulty sleeping alone. However, co-sleeping may worsen their anxiety over time rather than resolve their sleep challenges. Although co-sleeping can offer immediate comfort by alleviating the child’s anxiety in the short term, it may inadvertently lead to negative reinforcement, potentially heightening their anxiety in the long run [10].

In conclusion, the complex nature of co-sleeping requires a more nuanced approach in both research and practice. The significant variations in co-sleeping prevalence, particularly between Western and non-Western cultures, highlight the need for culturally sensitive guidelines. Future research should focus on longitudinal studies to better understand the developmental timing, pattern variability, and potential subgroup vulnerabilities associated with co-sleeping. Additionally, investigating parental factors, such as sleep-related beliefs and anxiety, may provide valuable insights into the dynamics of co-sleeping and its impact on child sleep patterns. By adopting a more comprehensive and culturally informed perspective, researchers and clinicians can develop more effective strategies to address sleep-related issues in children while respecting diverse family practices and cultural norms.